In order for lightening a load relative to the environment, weight reduction of an engine, etc. are desired and there is an increase in the application of an aluminum alloy. Also, in view of a demand for an improvement in productivity, a reduction in casting time by the pressure casting is sought.
However, there is a problem of shrinkage cavity in the casting, and proposals for solving the problem are made for example by patent references 1 to 3. In patent reference 1, there is proposed the art that an upper die, a lower die and a slide die each are comprised of materials different in heat conductivity, and the die of low heat conductivity is used as the die corresponding to a thin section of a casting product so as to carry out directional solidification.
In patent reference 2 and patent reference 3, there is also proposed the art that an upper die is comprised of a copper alloy of high heat conductivity, a lower die is comprised of metallic material of carbon tool steel having lower heat conductivity than the upper die, and a slide die is comprised of metallic material having intermediate heat conductivity relative to the upper die and the lower die so as to carry out the directional solidification by the use of the difference in heat conductivity.    Patent reference 1: Japanese patent application publication No. H01-237067.    Patent reference 2: Japanese patent application publication No. H01-053755.    Patent reference 3: Japanese patent application publication No. H01-053757.